Question
I have a lemon tree in the back yard of the house we bought two years ago.
The first year we got lots of healthy lemons. Last winter I noticed white spots
on the bark and some of the lemons were pitted with tiny black spots. Now
most of the mature lemons are covered in a whitish grey material (fungus?).

1) What do you think this is?
2) How do I treat it?
3) If I wash the lemons that have no apparent fungus on them, are they still
edible?

Should also mention I live in Northern California, and we've had pretty
extreme weather here over the last year and a half.

Thanks!  

Answer
Hi Jennifer,

Try to give me some more information.  You mention that you had first noticed "white spots" on the bark.  Were these regular in shape, i.e. were they nearly circular or ovular in shape,~5mm (1/16")in diameter?  If so, this is a scale insect infestation, a common insect pest in citrus.

The black spots on the lemon fruit is not related to scale insect infestation, Are there also be spots on the leaves? These are more difficult to see than on the fruit. Are there any halos around the blemishes?    

Can you describe the whitish grey "material"?  If you hold a piece of white paper beneath the fruit and tap gently, do you see any "powder"?  Is the material more stringlike, like a spider's web?  

Give me as much information as possible, and I will try to help out.

Thanks,

John